why do we have two sets of teeth

One of the most amazing parts of being a pediatric dentist is having the opportunity to teach kids about their oral health. Providing them with an extra education about how their teeth work and what they can do to keep them healthy is the most important thing we do as dentists. After all, бweБre setting them up for a lifetime of healthy smiles. As your child climbs to the ages of six and seven, youБll notice those cute little baby teeth start falling out. As your child sheds these teeth they may be wondering what is happening to them and why on earth their teeth are falling out?! You can rest assure them itБs normal and hereБs why. We are born with no teeth, and then when we get to 6 months old our deciduous teeth come in. ThatБs a big word for baby, or primary teeth. This set of teeth is extremely important. They help us learn to speak, teach us how to eat and give our jaws some nice guidelines to develop around. One of the other important aspects of baby teeth is they give kids the opportunity to learn how to take care of their teeth, so that when their permanent teeth come in, theyБre able to keep them for their entire life. Humans grow, and as we grow so do our jaws. What once fit perfectly now isnБt so snug. Underneath our primary teeth our permanent teeth have been forming. The primaries hold the spaces for permanent teeth and when the jaw is big enough for the permanent teeth to come out, the push the primaries out of the way. The result are those funny gaps. ItБs no surprise or mystery why we have two sets of teeth. Our БtrainerБ teeth are there to help us grow and learn so that when our permanent teeth come in we know how to take care of them.


ItБs so important to take care of both sets of teeth even though one set is going to fall out. If you have any questions about how to teach your kids the important lessons of proper oral hygiene, swing on by today. We love teaching kids about their teeth and telling them all about how to keep them healthy.
Actually, you re asking the wrong question. Let me explain. We have two sets of teeth, like most mammals (some mammals, such as rodents, only have one set of teeth, and still others, such as baleen whales, have none at all). But our distant ancestors, hundreds of millions of years ago, had the ability to grow endless sets of teeth. Today, we see this ability retained in modern fish, amphibians, and reptiles. Now, replacement teeth seem to grow in a really stereotyped manner. There s a layer of cells in the mouth that lay just medial (tonguewards) of the tooth, called the successional lamina. In mammals, the successional lamina is contained within the cavity that holds the root (the alveolus) but in reptiles and amphibians, the successional lamina will often be part of the medial gumline. The successional lamina contains stem cells as well as epithelial cells. Periodically, the successional lamina will form a pocket, that will then fold up in various ways, then differentiate into an enamel organ and pulp cavity, which will then produce a tooth. The remainder of the successional lamina will then proliferate to create more successional lamina, and will later repeat the whole cycle.


In mammals, this is disrupted. The successional lamina forms a replacement tooth (your adult tooth) but it does not form a new successional lamina. This is not the case in all people; some people are able to produce a third or even a fourth set of teeth, but this is the case in most people, and indeed in most mammals. So now we know how humans came to have only two sets of teeth. But why? It s kind of ridiculous, considering that a tooth really doesn t last very long, even with modern dentistry. However, our early mammal ancestors were small and likely had short lifespans, much like modern shrews, rodents, possums, and other small furry creatures. This was, of course, probably also the case for many of our early nearly-mammalian ancestors, and our early somewhat-mammalian ancestors, and before that our early almost-amniote (egg-laying) ancestors, our early almost-amphibian ancestors, and so on. But our early mammalian ancestors did something special; they fed their offspring milk. The benefit of milk is that it doesn t require an adult dentition to consume, and it contains a lot of energy, minerals, and other things the body needs to grow. So baby mammals grow up really, really fast. Furthermore, as soon as a baby mammal reaches sexual maturity, it stops growing. So, a baby reptile or amphibian or almost-mammal might take a few years to reach adulthood, and during that time, it s going to be using its teeth to eat plants, or insects, or other reptiles, amphibians, or almost mammals, and once it becomes an adult, it s going to keep growing for a while longer, although it will slow down considerably.


So, a reptile, amphibian, or almost-mammal is going to need to keep on replacing those teeth as they grow, because the teeth that were good for catching small insects when they re a few months old won t be all that good for catching small amphibians or reptiles when they re a year or two old, and so on, so they need to keep on making more teeth and larger teeth as they grow. A mammal, however, doesn t need to do that. That first generation of teeth (baby teeth) are good enough to get it through the growing stage of its life, and when the mammal reaches adulthood, it gets its adult teeth, at which point it s as large as it s going to get, and thus will never need to replace its teeth. And because our early mammal ancestors probably only lived a couple of years at most, they didn t have to worry about cavities too much, because by the time their adult teeth were too damaged to use well, they had likely produced plenty of little baby early mammal ancestors, and, more importantly, had probably been devoured by a small dinosaur anyways. So our early mammal ancestors did away with additional replacement teeth, because they simply didn t need them. They still needed those baby teeth, and they still needed adult teeth, so that s why we have two generations of teeth. tl;dr: baby and adult teeth are holdovers from our reptile-like ancestors, who replaced their teeth continuously throughout their lifespan. We lost the continuously but still kept the replacement.

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